drm/atomic: Call ww_acquire_done after check phase is complete

We want to make sure that no one tries to acquire more locks and
states, and ww mutexes provide debug facilities for that. So use them.

v2: Only call acquire_done when ->atomic_check was successful to avoid
falling over an -EDEADLK (spotted by Maarten).

Cc: Rob Clark <robdclark@gmail.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>